Tubular heater terminal



May 10, 1932- c. B. BACKER 1,857,614

TUBULAR HEATER TERMINAL Filed Dec. 17, 1929 lNVENTOR Chr/sf/an B. Baa/rer- ATTORNEY Patented May 10, 1932 UNITED STATES PATENT orrlca TUBULAR HEATER TERMINAL Application filed December 17, 1929, Serial No. 414,781, and in Canada Augult 2}, 1829.

My invention relates to tubular electric heating units and, more particularly, to terminal structures for such heating umts.

An object of my invention is to provide a 5 relatively simple and highly efficient terminal structure for a tubular heating unit that shall embody 'a minimum number of parts and that shall be highly efiicient in operation.

Another objectof my invention is to pro- 19 vide a terminal structure for a tubular heating unit that shall be adapted to remain in its proper operative position 'during repeated and long continued cycles of operation without losing its air and fluid-tight characteristics.

in practicing my invention, I provide a tubular heating unit embodyingJ an outer metal tube, a resistor within the tu e and separated therefrom by crystalline electric-insulating material generated in situ, with a terminal structure embodying a terminal tube located in an expanded end portion of the metal tube, a pair of spaced bushings of electrio-insulating material on said terminal tube and adapted to be located within the expanded end portion of the metal tube, a filling of granular electric-insulating material around the terminal tube between the bushings and within the expanded portion of the 80 metal tube and means including collars on said terminal tube for holding it and the bushings in proper and predetermined operative positions relatively to each other.

In the single sheet of drawings,

Figure 1 is a View in longitudinal section through an end portion and a part of the body portion of a tubular heating unit embodying my improved terminal structure, and

Fig. 2 is a similar view of a modified form of terminal structure eml'iodyin my invention.

The terminal structure to be hereinafter described in detail is particularly applicable to tubular: heating units in which the electric-insulating and heat-conducting material, located between a resistor member and an outer metal tube casing, is generated in situ by the method more particularly set forth in my U. S. Reissue Patent No. 16,340. I

have heretofore found it relatively diflicult to provide a properly operative terminal structure for heating units of this kind, particularly so, if the diameter of the outer metal tuble was on the order of one-quarter of aninc Referring more particularly to Fig. 1 of the drawings, I have there illustrated a body portion 11 of a metaltube which may be made of any one of a number of different kinds of materials, such as steel, stainless steel or one of the numerous corrosion-resistant alloys which may now be purchased in the open market. A helically wound resistor member 12 is located within the body portion 11 and a hard, dense crystalline mass 13 of heat-conducting and electricinsulating material spaces the resistor 12 from the inner walls of the tube 11.

Briefly, the process of generating the electric-insulating mass comprises providing within and without the helically wound resistor member initially metallic magnesium and then subjecting the assembly, including the tube 11, the resistor )12 and the metallic magnesium, to' the action of high temperature steam for a predetermined length of time, whereby the magnesium is converted into a hard solid crystalline mass of magnesium hydroxide which may be changed into magnesium oxide by subjecting it to a relatively high temperature to drive out the included water. I have described a novel method of doing this in my copending application, Serial No. 414,733, filed of even date herewith.

When the diameter of the tube 11 is relatively small, approximately one-quarter inch, l find it highly desirable to expand the end portions of the metal tube to a somewhat larger diameter, as indicated by a portion 14: in Fig. 1 of the drawings. The resistor member 12, which is of helical form in the body portion 11, has been straightened at the end portions as is shown at 16 in the drawings.

In order to provide a substantially airtight plug or filling in the outer end 0rtion 11, I prefer to compact a mass 1 of granular electric-insulating magnesium oxide in place, eflecting this by means ofa tubular hammer. The dividin line between the electric-insulating materia s 13 and 17 is indicated by the broken line 18, although this line is notin'tended to show any one limiting position of the junction of the two different kinds of insulation.

After the mass 17 has been hammered or compacted into place by longitudinal 11ammer blows as set forth above, I locate around the straight art 16 of the resistor a terminal tube 19 whic is made of a high temperature resisting metal, such as some alloy steel or nickel or a combination of nickel and copper known as Monel metal. The inner portion of the terminal tube 19 is provided with a collar 21 which may be brazed thereon or be integral therewith as may be desirable.

A pair of bushings 22 and 23 of a suitable electric-insulating material such as lava, are cemented on the inner end portion of the terminal tube 19 and serve to center the inner end of the terminal tube within the expanded portion 14.

A mass 24 of a granular electric-insulating material similar to the material indicated by the numeral 17 is then compacted in place adjacent to the outer end of bushing 23, whereby I provide. a further air-tight seal for the lava bushings 22 and 23, the highly compacted mass 24 serving, of course, as an additional bushing whose effect is added to that of bushin 17.

An outer bus 'ng 26 of electric-insulatin material is then located in the outer end 0 the ex anded portion 14, the bushing 26 having a ar r diameter in that portion outside of the tu e thanvin that portion inside the tube, in order to prevent movement of the bushing inwardly of the end of the tube.

In order to prevent outward movement of the bushing 26 on the terminal tube 19, I provide a second collar 27 which may be brazed on the terminal tube in order to prevent movement of the bushin 26 away from the metal tube portion 14. the outer end of the resistor wire 16 to or in the outer end of the terminal tube 19, as shown at 28.

Referring to Fig. 2 of the drawings, I have indicated like parts by the same numerals as were used in Fig. 1 of the dra wings'and would point out that the inner portion of the terminal structure difi'ers slightly from that shown in Fig. 1 in that only one bushing 31 of a suitable electric-insulating material is used instead of the two bushings 22 and 23 of Fig. 1. The single bushing 31 is cemented to the terminal tube 19 as was hereinbefore set forth for the two bushings of Fig. 1. In all other respects the terminal structure comprises the same parts and is made in substantially the same manner and operates in substantially the manner as hereinbefore set forth for' the terminal structure of Fig. 1.

finally braze The use of a terminal tube means, of course,

that its diameter is somewhat. lar r than the diameter of the wire, and 'theushings of electric-insulating material cooperate with the terminal tube to hold it coaxially in the portion 14. The compacted ortions- 17 and 24 of granular electric-insu atin material are effective to provide a seal for t e portions located inside thereof which are air-ti ht even through repeated c cles of operation when the body portion of the heater will be operated at relatively high temperature, which will be partially reflected in a relatively hlgh temperature in the terminal portion, which tem rature, however, is not as hi h as in the b0 lyeportion because of the use of t e terminal tu and the slightly enlarged diameter of the end portion 14.

The device embodying my invention thus rovides a relativel simple, compact, and ighly eflicient terminal structure for a tubular heating unit of relatively small diameter, which terminal structure comprises relatively few parts and will continue to operate satisfactorily over lon periods of time and through repeated cyc es of heating to a high temperature and cooling to a room temperature.

Various modifications may be made in the device embodying m invention without departing from the spirit and scope thereof, and

I desire, therefore, that only such limitations 7 shall be placed thereon as are imposed by the prior art and are set forth in the appended claims.

I claim as my invention:

1. A terminal structure for a tubular heating unit having an outer metal tube, a resistor ing material therebetween, said terminal structure including a tubular terminal surrounding the end portion of the resistor and projecting beyond the end of the tube and having a collar thereon adj aoent to the inner end thereof, a bushing of electric-insulating material on said tubular terminal and prevented from longitudinal movement in one direction relatively thereto by said collar, an outer bushing of electric-insulating material interfitting with the end of the metal tube, a second collar on said tubular terminal for holding the outer bushing in proper position, and a brazed connection between the outer ends of the resistor wire and of the tubular terminal.

2. A terminal structure for a tubular heating unit having an outer metal tube, a resistor therein including an end portion extending beyond the end of the tube and electric-insulating material therebetween, said terminal bushin of electric-insulating material on said tu ular terminal for holding the tubular terminal coaxial with the metal tube, granular electric-insulating material in the metal tube between the bushings, collars on said tubular terminal for holdlng the bushings and the tubular terminal in predetermined operative positions relatively to each other, and a solid electrical connection between the end of the tubular terminal and the end portion of the resistor.

3. The method of making a terminal structure for a tubular heater of relatively small diameter and embodying an outer metal tube,

a resistor therein having an end portion extending beyond the end of the tube and electric-insulating material therebetween, which includes expanding an end portion of the metal tube, locating a terminal tube around the projecting end portion of the resistor and in said expanded portion of the metal tube and projecting therefrom, compacting granular electric-insulating material around an inner portion of the terminal tube, locatin a bushing in the outer end of the expan ed metal tube to protect the compacted granular material, locating a collar on the outer end portion of the terminal tube to hold the bushing in the end of the metal tube and elecao trically connecting the projecting end of the resistor to the pro ecting end of the terminal tube.

In testimony whereof, I have hereunto subscribed my name this 9th day of December,

CHRISTIAN BERGH BACKER. 

